This invention relates to pultrusion dies and, more particularly, to a die for forming longitudinally serrated, fiber-reinforced plastic rods used in the assembly of electric motors. In the manufacture of electric motors nonconducting rods are driven into the stator to hold the windings out of place while the varnish is being baked. Various types of rods have been employed, such as tapered wooden pegs, and fiber-reinforced, serrated rods. Serrated rods are desirable in that they can be molded by a pultrusion technique on an economical basis. The points of the serrations are abraded away as the rod is driven in place to form an effective wedge without tapering the rod, which would be impossible in a pultrusin technique. However, since the rod has an outside diameter of about 0.093 inch to about 0.187 inch, the pultrusion die must be extremely small, and therefore as a practical matter, it is not possible to machine the serrations into the die cavity.
Rather than machine the cylindrical inner surface of an elongated die, it has been proposed in U.S. Pat. No. 1,398,412 to make a serrated die cavity by locking together a plurality of axially extending staves having abutting sides disposed in radial planes and inner surfaces configured to provide longitudinal flutes in the surface of a generally cylindrical or rodlike member to be molded. Two or more such die block assemblies are joined on radially disposed parting planes. For a pultrusion die having the dimensions noted above, such an arrangement would be prohibitively expensive, due to the necessary precise machining of the nonparallel, radially disposed, abutting sides of the staves.